Gas turbine engines are commonly equipped with pluggable holes in their outer casings to allow use of borescopes. These are fiber-optic devices that allow visual inspection of the interior of the engine without disassembling it, which is a major advantage to operators. However, the presence of the hole in the casing tends to locally disrupt the smooth flow of air through the engine along the casing walls. It can also be a path of leakage of high-pressure air into areas where it does not contribute to the engine's performance. This is true even though the ports are filled with a plug that is removed for borescope access, since the fit of the plug may not be—and normally is not—perfect.
Because the borescope access hole typically penetrates more than one component of a gas turbine engine, some allowance must be made for variations in the location of the hole in each of these components. This is usually accomplished by making the holes larger than they would otherwise need to be for borescope access. The increased size of the holes aggravates the airflow disruption and leakage problem.
One common design for a gas turbine engine compressor uses multiple segments of stator vanes inserted into the casing. Design features, such as anti-rotation lugs, fix the stator segments into the casing circumferentially, preventing them from spinning in place. Although this approach provides a number of advantages, it adds a part into the “stack” of engine parts through which the borescope access port must penetrate. The port's location is normally fixed by the locations and designs of the engine components on the outside of the casings, and of the aircraft or other location in which the engine is installed. The further away from the anti-rotation lugs the stator segments' borescope port is placed, the more variation there can be in the port's location relative to the external features, which usually are used to locate the removable plug itself.
Accordingly, it is an object of the present invention to provide a borescope port and gas turbine engine incorporating such port that overcomes the above-mentioned drawbacks and disadvantages.